1. Field of the Disclosure
The present disclosure relates generally to electrophotographic imaging devices such as a printer or multifunction device having printing capability, and in particular to a toner level sensor in a toner container of the imaging device.
2. Description of the Related Art
Image forming devices such as copiers, laser printers, facsimile machines and the like typically use one or more toner containers to hold toner supply used for image forming processes. In some image forming devices, a large toner supply is provided in a reservoir in a toner cartridge that mates with a separate imaging unit. The imaging unit may include a sump that holds a smaller amount of toner, enough to ensure toner is adequately supplied by a toner adder roll and a developer roll to a photoconductive drum. As toner within the imaging unit sump is depleted due to printing operations, additional toner is transferred from the toner cartridge to the imaging unit sump.
To ensure satisfactory operation of the imaging unit to transfer toner, the toner level within the imaging unit sump is maintained at a proper level. For example, if the imaging unit sump holds too much toner, toner may pack in the imaging unit sump, leak out of the ports and eventually break other components located inside and outside the imaging unit. If the toner level in the imaging unit sump gets too low, the toner adder roll may starve, causing a doctor blade of the imaging unit to film and damage the developer roll which may eventually impair the future performance of the imaging unit. As such, it is desirable to know the toner level in the imaging unit sump so as to effectively determine when to move toner from toner cartridge to the imaging unit sump.
Some methods for determining toner level in a container use estimates of toner use and accumulation based on print or time counts. However, these methods may not be accurate due to variability in factors such as the environment, developer roll age, toner patch sensing cycles, and toner transfer parameters.
Other known techniques for sensing or determining toner level include the use of electrical sensors that measure the motive force required to drive an agitator within a toner container, optical devices including mirrors and toner dust wipers in a container, and other opto-electromechanical devices such as a flag that moves with the toner level to actuate a sensor that triggers only when the volume reaches a predetermined level. Unfortunately, the addition of moving hardware increases component complexity and opportunities for errors.
Another existing solution provides two parallel plates disposed within the interior of a toner container for detecting toner volume levels. The two parallel plates form a capacitor having a capacitance that varies with the amount of toner existing between the two parallel plates. This solution, however, may not provide a sufficiently accurate means for detecting toner levels in a toner container because of lack of sensitivity to small changes in toner level.
Based upon the foregoing, there is a need for toner level sensing that is more sensitive to changes in toner level within a toner container, without substantially increasing manufacturing costs.